// Copyright 2014-2021 The winit contributors
// Copyright 2021-2023 Tauri Programme within The Commons Conservancy
// SPDX-License-Identifier: Apache-2.0

use std::{
  cell::{RefCell, RefMut},
  collections::VecDeque,
  fmt::{self, Debug},
  hint::unreachable_unchecked,
  mem,
  rc::{Rc, Weak},
  sync::{
    atomic::{AtomicBool, Ordering},
    Mutex, MutexGuard,
  },
  time::Instant,
};

use cocoa::{
  appkit::{NSApp, NSApplication, NSWindow},
  base::{id, nil},
  foundation::{NSAutoreleasePool, NSSize},
};
use objc::runtime::{Object, BOOL, NO, YES};

use crate::{
  dpi::LogicalSize,
  event::{Event, StartCause, WindowEvent},
  event_loop::{ControlFlow, EventLoopWindowTarget as RootWindowTarget},
  platform::macos::ActivationPolicy,
  platform_impl::{
    get_aux_state_mut,
    platform::{
      event::{EventProxy, EventWrapper},
      event_loop::{post_dummy_event, PanicInfo},
      observer::{CFRunLoopGetMain, CFRunLoopWakeUp, EventLoopWaker},
      util::{IdRef, Never},
      window::get_window_id,
    },
  },
  window::WindowId,
};

lazy_static! {
  static ref HANDLER: Handler = Default::default();
}

impl<'a, Never> Event<'a, Never> {
  fn userify<T: 'static>(self) -> Event<'a, T> {
    self
      .map_nonuser_event()
      // `Never` can't be constructed, so the `UserEvent` variant can't
      // be present here.
      .unwrap_or_else(|_| unsafe { unreachable_unchecked() })
  }
}

pub trait EventHandler: Debug {
  // Not sure probably it should accept Event<'static, Never>
  fn handle_nonuser_event(&mut self, event: Event<'_, Never>, control_flow: &mut ControlFlow);
  fn handle_user_events(&mut self, control_flow: &mut ControlFlow);
}

struct EventLoopHandler<T: 'static> {
  callback: Weak<RefCell<dyn FnMut(Event<'_, T>, &RootWindowTarget<T>, &mut ControlFlow)>>,
  window_target: Rc<RootWindowTarget<T>>,
}

impl<T> EventLoopHandler<T> {
  fn with_callback<F>(&mut self, f: F)
  where
    F: FnOnce(
      &mut EventLoopHandler<T>,
      RefMut<'_, dyn FnMut(Event<'_, T>, &RootWindowTarget<T>, &mut ControlFlow)>,
    ),
  {
    if let Some(callback) = self.callback.upgrade() {
      let callback = callback.borrow_mut();
      (f)(self, callback);
    } else {
      panic!(
        "Tried to dispatch an event, but the event loop that \
                owned the event handler callback seems to be destroyed"
      );
    }
  }
}

impl<T> Debug for EventLoopHandler<T> {
  fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
    formatter
      .debug_struct("EventLoopHandler")
      .field("window_target", &self.window_target)
      .finish()
  }
}

impl<T> EventHandler for EventLoopHandler<T> {
  fn handle_nonuser_event(&mut self, event: Event<'_, Never>, control_flow: &mut ControlFlow) {
    self.with_callback(|this, mut callback| {
      if let ControlFlow::ExitWithCode(code) = *control_flow {
        let dummy = &mut ControlFlow::ExitWithCode(code);
        (callback)(event.userify(), &this.window_target, dummy);
      } else {
        (callback)(event.userify(), &this.window_target, control_flow);
      }
    });
  }

  fn handle_user_events(&mut self, control_flow: &mut ControlFlow) {
    self.with_callback(|this, mut callback| {
      for event in this.window_target.p.receiver.try_iter() {
        if let ControlFlow::ExitWithCode(code) = *control_flow {
          let dummy = &mut ControlFlow::ExitWithCode(code);
          (callback)(Event::UserEvent(event), &this.window_target, dummy);
        } else {
          (callback)(Event::UserEvent(event), &this.window_target, control_flow);
        }
      }
    });
  }
}

#[derive(Default)]
struct Handler {
  ready: AtomicBool,
  in_callback: AtomicBool,
  control_flow: Mutex<ControlFlow>,
  control_flow_prev: Mutex<ControlFlow>,
  start_time: Mutex<Option<Instant>>,
  callback: Mutex<Option<Box<dyn EventHandler>>>,
  pending_events: Mutex<VecDeque<EventWrapper>>,
  pending_redraw: Mutex<Vec<WindowId>>,
  waker: Mutex<EventLoopWaker>,
}

unsafe impl Send for Handler {}
unsafe impl Sync for Handler {}

impl Handler {
  fn events(&self) -> MutexGuard<'_, VecDeque<EventWrapper>> {
    self.pending_events.lock().unwrap()
  }

  fn redraw<'a>(&'a self) -> MutexGuard<'a, Vec<WindowId>> {
    self.pending_redraw.lock().unwrap()
  }

  fn waker(&self) -> MutexGuard<'_, EventLoopWaker> {
    self.waker.lock().unwrap()
  }

  fn is_ready(&self) -> bool {
    self.ready.load(Ordering::Acquire)
  }

  fn set_ready(&self) {
    self.ready.store(true, Ordering::Release);
  }

  fn should_exit(&self) -> bool {
    matches!(
      *self.control_flow.lock().unwrap(),
      ControlFlow::ExitWithCode(_)
    )
  }

  fn get_control_flow_and_update_prev(&self) -> ControlFlow {
    let control_flow = self.control_flow.lock().unwrap();
    *self.control_flow_prev.lock().unwrap() = *control_flow;
    *control_flow
  }

  fn get_old_and_new_control_flow(&self) -> (ControlFlow, ControlFlow) {
    let old = *self.control_flow_prev.lock().unwrap();
    let new = *self.control_flow.lock().unwrap();
    (old, new)
  }

  fn get_start_time(&self) -> Option<Instant> {
    *self.start_time.lock().unwrap()
  }

  fn update_start_time(&self) {
    *self.start_time.lock().unwrap() = Some(Instant::now());
  }

  fn take_events(&self) -> VecDeque<EventWrapper> {
    mem::take(&mut *self.events())
  }

  fn should_redraw(&self) -> Vec<WindowId> {
    mem::take(&mut *self.redraw())
  }

  fn get_in_callback(&self) -> bool {
    self.in_callback.load(Ordering::Acquire)
  }

  fn set_in_callback(&self, in_callback: bool) {
    self.in_callback.store(in_callback, Ordering::Release);
  }

  fn handle_nonuser_event(&self, wrapper: EventWrapper) {
    if let Some(ref mut callback) = *self.callback.lock().unwrap() {
      match wrapper {
        EventWrapper::StaticEvent(event) => {
          callback.handle_nonuser_event(event, &mut *self.control_flow.lock().unwrap())
        }
        EventWrapper::EventProxy(proxy) => self.handle_proxy(proxy, callback),
      }
    }
  }

  fn handle_user_events(&self) {
    if let Some(ref mut callback) = *self.callback.lock().unwrap() {
      callback.handle_user_events(&mut *self.control_flow.lock().unwrap());
    }
  }

  fn handle_scale_factor_changed_event(
    &self,
    callback: &mut Box<dyn EventHandler + 'static>,
    ns_window: IdRef,
    suggested_size: LogicalSize<f64>,
    scale_factor: f64,
  ) {
    let mut size = suggested_size.to_physical(scale_factor);
    let new_inner_size = &mut size;
    let event = Event::WindowEvent {
      window_id: WindowId(get_window_id(*ns_window)),
      event: WindowEvent::ScaleFactorChanged {
        scale_factor,
        new_inner_size,
      },
    };

    callback.handle_nonuser_event(event, &mut *self.control_flow.lock().unwrap());

    let physical_size = *new_inner_size;
    let logical_size = physical_size.to_logical(scale_factor);
    let size = NSSize::new(logical_size.width, logical_size.height);
    unsafe { NSWindow::setContentSize_(*ns_window, size) };
  }

  fn handle_proxy(&self, proxy: EventProxy, callback: &mut Box<dyn EventHandler + 'static>) {
    match proxy {
      EventProxy::DpiChangedProxy {
        ns_window,
        suggested_size,
        scale_factor,
      } => {
        self.handle_scale_factor_changed_event(callback, ns_window, suggested_size, scale_factor)
      }
    }
  }
}

pub enum AppState {}

impl AppState {
  pub fn set_callback<T>(
    callback: Weak<RefCell<dyn FnMut(Event<'_, T>, &RootWindowTarget<T>, &mut ControlFlow)>>,
    window_target: Rc<RootWindowTarget<T>>,
  ) {
    *HANDLER.callback.lock().unwrap() = Some(Box::new(EventLoopHandler {
      callback,
      window_target,
    }));
  }

  pub fn exit() -> i32 {
    HANDLER.set_in_callback(true);
    HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::LoopDestroyed));
    HANDLER.set_in_callback(false);
    HANDLER.callback.lock().unwrap().take();
    if let ControlFlow::ExitWithCode(code) = HANDLER.get_old_and_new_control_flow().1 {
      code
    } else {
      0
    }
  }

  pub fn launched(app_delegate: &Object) {
    apply_activation_policy(app_delegate);
    unsafe {
      let ns_app = NSApp();
      window_activation_hack(ns_app);
      let ignore = if get_aux_state_mut(app_delegate).activate_ignoring_other_apps {
        YES
      } else {
        NO
      };
      ns_app.activateIgnoringOtherApps_(ignore);
    };
    HANDLER.set_ready();
    HANDLER.waker().start();
    HANDLER.set_in_callback(true);
    HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::NewEvents(
      StartCause::Init,
    )));
    HANDLER.set_in_callback(false);
  }

  pub fn wakeup(panic_info: Weak<PanicInfo>) {
    let panic_info = panic_info
      .upgrade()
      .expect("The panic info must exist here. This failure indicates a developer error.");
    // Return when in callback due to https://github.com/rust-windowing/winit/issues/1779
    if panic_info.is_panicking() || !HANDLER.is_ready() || HANDLER.get_in_callback() {
      return;
    }
    let start = HANDLER.get_start_time().unwrap();
    let cause = match HANDLER.get_control_flow_and_update_prev() {
      ControlFlow::Poll => StartCause::Poll,
      ControlFlow::Wait => StartCause::WaitCancelled {
        start,
        requested_resume: None,
      },
      ControlFlow::WaitUntil(requested_resume) => {
        if Instant::now() >= requested_resume {
          StartCause::ResumeTimeReached {
            start,
            requested_resume,
          }
        } else {
          StartCause::WaitCancelled {
            start,
            requested_resume: Some(requested_resume),
          }
        }
      }
      ControlFlow::ExitWithCode(_) => StartCause::Poll, //panic!("unexpected `ControlFlow::Exit`"),
    };
    HANDLER.set_in_callback(true);
    HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::NewEvents(cause)));
    HANDLER.set_in_callback(false);
  }

  // This is called from multiple threads at present
  pub fn queue_redraw(window_id: WindowId) {
    let mut pending_redraw = HANDLER.redraw();
    if !pending_redraw.contains(&window_id) {
      pending_redraw.push(window_id);
    }
    unsafe {
      let rl = CFRunLoopGetMain();
      CFRunLoopWakeUp(rl);
    }
  }

  pub fn handle_redraw(window_id: WindowId) {
    HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::RedrawRequested(window_id)));
  }

  pub fn queue_event(wrapper: EventWrapper) {
    let is_main_thread: BOOL = unsafe { msg_send!(class!(NSThread), isMainThread) };
    if is_main_thread == NO {
      panic!("Event queued from different thread: {:#?}", wrapper);
    }
    HANDLER.events().push_back(wrapper);
  }

  pub fn queue_events(mut wrappers: VecDeque<EventWrapper>) {
    let is_main_thread: BOOL = unsafe { msg_send!(class!(NSThread), isMainThread) };
    if is_main_thread == NO {
      panic!("Events queued from different thread: {:#?}", wrappers);
    }
    HANDLER.events().append(&mut wrappers);
  }

  pub fn cleared(panic_info: Weak<PanicInfo>) {
    let panic_info = panic_info
      .upgrade()
      .expect("The panic info must exist here. This failure indicates a developer error.");
    // Return when in callback due to https://github.com/rust-windowing/winit/issues/1779
    if panic_info.is_panicking() || !HANDLER.is_ready() || HANDLER.get_in_callback() {
      return;
    }
    HANDLER.set_in_callback(true);
    HANDLER.handle_user_events();
    for event in HANDLER.take_events() {
      HANDLER.handle_nonuser_event(event);
    }
    HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::MainEventsCleared));
    for window_id in HANDLER.should_redraw() {
      HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::RedrawRequested(window_id)));
    }
    HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::RedrawEventsCleared));
    HANDLER.set_in_callback(false);
    if HANDLER.should_exit() {
      unsafe {
        let app: id = NSApp();
        let pool = NSAutoreleasePool::new(nil);
        let () = msg_send![app, stop: nil];
        // To stop event loop immediately, we need to post some event here.
        post_dummy_event(app);
        pool.drain();
      };
    }
    HANDLER.update_start_time();
    match HANDLER.get_old_and_new_control_flow() {
      (ControlFlow::ExitWithCode(_), _) | (_, ControlFlow::ExitWithCode(_)) => (),
      (old, new) if old == new => (),
      (_, ControlFlow::Wait) => HANDLER.waker().stop(),
      (_, ControlFlow::WaitUntil(instant)) => HANDLER.waker().start_at(instant),
      (_, ControlFlow::Poll) => HANDLER.waker().start(),
    }
  }
}

/// A hack to make activation of multiple windows work when creating them before
/// `applicationDidFinishLaunching:` / `Event::Event::NewEvents(StartCause::Init)`.
///
/// Alternative to this would be the user calling `window.set_visible(true)` in
/// `StartCause::Init`.
///
/// If this becomes too bothersome to maintain, it can probably be removed
/// without too much damage.
unsafe fn window_activation_hack(ns_app: id) {
  // Get the application's windows
  // TODO: Proper ordering of the windows
  let ns_windows: id = msg_send![ns_app, windows];
  let ns_enumerator: id = msg_send![ns_windows, objectEnumerator];
  loop {
    // Enumerate over the windows
    let ns_window: id = msg_send![ns_enumerator, nextObject];
    if ns_window == nil {
      break;
    }
    // And call `makeKeyAndOrderFront` if it was called on the window in `UnownedWindow::new`
    // This way we preserve the user's desired initial visiblity status
    // TODO: Also filter on the type/"level" of the window, and maybe other things?
    if ns_window.isVisible() == YES {
      trace!("Activating visible window");
      ns_window.makeKeyAndOrderFront_(nil);
    } else {
      trace!("Skipping activating invisible window");
    }
  }
}
fn apply_activation_policy(app_delegate: &Object) {
  unsafe {
    use cocoa::appkit::NSApplicationActivationPolicy::*;
    let ns_app = NSApp();
    // We need to delay setting the activation policy and activating the app
    // until `applicationDidFinishLaunching` has been called. Otherwise the
    // menu bar won't be interactable.
    let act_pol = get_aux_state_mut(app_delegate).activation_policy;
    ns_app.setActivationPolicy_(match act_pol {
      ActivationPolicy::Regular => NSApplicationActivationPolicyRegular,
      ActivationPolicy::Accessory => NSApplicationActivationPolicyAccessory,
      ActivationPolicy::Prohibited => NSApplicationActivationPolicyProhibited,
    });
  }
}
